Membrane Bioreactor (MBR) systems have been increasingly used to treat waste. MBR systems utilise a reactor having a chamber comprising activated sludge and membrane separation equipment. The activated sludge contains microorganisms that are able to remove contaminant or undesirable species present in waste water. Solids are removed from the treated water using the membrane separation equipment, which due to its pore size, may also selectively remove contaminant species remaining in solution.
MBR systems exhibit several advantages compared to the traditional activated sludge processes, such as high effluent quality, limited space requirement and as an extension of existing waste water treatment plants.
A common problem associated with MBR systems is that the activated sludge causes fouling of the membrane. Membrane fouling may be attributed to precipitation, deposition or adsorption of solute species or particles onto the surfaces and/or into the pores of the membrane. Membrane fouling may be biological in nature and foulant species may comprise bacterial floc and supernatant species including extracellular polymeric substances. Membrane fouling leads to significant flux reduction through the membrane, higher transmembrane pressures and other operational inefficiencies.
Fouling of the membrane leads to the MBR system having to be shut down while the membranes is either cleaned and/or replaced.
There have been various attempts to circumvent fouling of membranes. For example, U.S. Pat. No. 4,636,473 discloses an elaborate anti-fouling device for preventing fouling on a membrane. The disadvantage with the anti-fouling system disclosed in U.S. Pat. No. 4,636,473 is that the system requires an elaborate housing arrangement and the application of reverse flow through the housing after a selected period of time, or after a selected pressure level has been reached, to avoid fouling of membrane surfaces and to prevent the formation of any appreciable caked substance on any membrane surface. This arrangement is costly to implement and is somewhat cumbersome to operate.
Li et al have attempted to improve membrane performance for wastewater treatment using aerobic granular sludge. Li et al seeded a submerged membrane bioreactor with granular sludge. The reactor was initially seeded with granular sludge up to a volumetric concentration of 8 gL−1. After 3-5 days of operation, the sludge concentration within the reactor increased to 15+/−2 gL−1 (i.e. the volumetric percentage concentration of the sludge in granular form was in the range of about 32% to about 38%). Once steady state was reached, the submerged membrane bioreactor was used to treat a synthetic wastewater consisting of glucose, protein and trace nutrients.
Li et al found improved permeate flux decline when the submerged membrane operated with about 32% to about 38% granular sludge relative to when the submerged membrane was operated with no sludge in granular form. However, the submerged membrane in Li et al was still subjected to pore blocking and the adsorption of colloids or solutes, which resulted in a significant decline in flux permeate.
There is a need to provide a water treatment system that avoids or at least ameliorates one or more of the disadvantages described above.